Traumas or diseases of the spine result in damage to individual vertebrae, intervertebral discs, or combinations thereof Different techniques are used for the surgical treatment, according to the indications, among which is the prosthesis of lost or removed fragments and their stabilization within the spinal column, otherwise called spondylodesis in surgical practice.
It is desirable to develop new and improved technical devices for spinal surgery providing improved functional attributes, increase of success rate, and the further extension of their applications.
Existing approaches include a technique of posteriorspondylodesis [1. Russian Patent 2,076,6541] employing a device consisting of a set of supporting implants that are cylindrical in shape, a stratified implant, and a bracing device, the brace is made of TiNi alloy with thermomechanical shape memory.
Cylindrical implants are positioned into sockets created between adjacent spinous processes of injured vertebral bodies. These are employed as supports between the vertebrae and serve to fix the injured segment of the spine.
The stratified implant is installed into a channel prepared in the cortical laminar layer and arched articular processes. Jointly and in contact with the cylindrical implants, it functions as a support and fixation device. The brace is used to brace the successive spinous processes and cylindrical implants, and it is also a dynamic element assisting in the correction of possible scoliotic deformities of the spine in the injured area.
The disadvantage of this device is its structural complexity and accompanying increased traumatism, the complexity of the operation required, and the high rigidity that results in the immobilization of the spinal segment.
A further device [2. Russian Patent 1,591,9781] for use in the surgical treatment of spinal injuries consists of a cylindrical rod made of porous TiNi alloy and fixing elements in the form of undulating curved clamps made of solid TiNi with shape-memory effect. In order to make the device compact and anatomically consistent, the fixing elements are installed into the longitudinal channels of the rod.
This device is used for the complete replacement of the vertebral body. It is fixed in place with fixing elements whose curved ends have been previously introduced into sockets in the upper segments of the inferior and lower segments of the superior adjacent intact vertebrae. During the installation, the shape-memory effect of the fixing elements is deployed. The disadvantage of this device is its high rigidity, which results in the immobilization of the spinal segment.
Another device [3. Russian Patent 1,526,6751] for the surgical treatment of the spine, which is used for partial or complete replacement of the vertebrae is illustrated in FIG. 1 and consists of a supporting element of cylindrical shape made of porous TiNi alloy, with fixing projections at its ends, one of which is immobile, while the other, at the opposite end, is movable in an axial direction and is provided with a spiral spring made of solid TiNi alloy with shape-memory effect. When performing the prosthesis of the spinal segment, the ends of the device are installed into sockets prepared in the proximal intact bone portion of the spine. The fixing projections prevent potential luxation of the spine at the site of the implantation.
The disadvantage of this device is the rigidity of its structure, which leads to the immobilization of the prosthetic segment.